The invention relates to a control or measuring unit of the joystick-type, comprising
a control or measuring means, for instance shaped as a handle, subjected to spring forces biasing said means towards a neural position,
a transmitting coil made of electrically conducting paths on a substrate or conducting sections of said substrate,
a number of receiving coils made by electrically conducting paths on a substrate or conducting sections of said substrate and positioned at three-dimensionally predetermined locations in relation to the transmitting coil.
A unit this type is described in the European Patent Application 0,166,467. In this prior art unit the transmitting coil and receiving coils are made onto one substrate which is located at a fixed position. The control of measuring means, in this case embodied as a handle, carries a ferrit body which in the neutral position is located centrally within the transmitting coil. If the control handle and therewith said ferrit body is moved from the neutral position, then the flux in one or more of the receiving coils will charge resulting into corresponding changing output signals of the receiving coils, which output signals can be used to detect the direction of movement of the ferrit body, respectively the control handle.
A disadvantage of the use of ferromagnetic material or ferrit materials is the fact that the relation between the field strength and induction (the so-called B-H curve) is not linear therefore imposing restrictions on the signal amplitude. Said non-linear B-H relation forms a source of inaccuracies, because this relation is dependent on various factors (time, temperature, hysteresis effect, remanence). Also on the long term this non-linear curve may result into a drifting signal transfer leading to an inaccurate signal detection.
A further disadvantage is that this prior art joystick has in principle only two freedom degrees for the control handle movement, that means two freedom degrees in which the movement can be detected, i.e. a rotation around the X-axis and a rotation around the Y-axis, whereby the imaginary X-Y-plane runs through the point of rotation of the control handle and is perpendicular to said control handle in the neutral position thereof. In many cases there is a need for more freedom degrees to be able to generate a corresponding larger number of various signals. In other cases the measuring unit will be embodied such that the unit can be used for measuring the residual function of handicapper users. Thereby it is important that other rotational or translational movements different from the usual x-rotation and y-rotation of the joystick are measurable.
An object of the invention is now to eliminate these disadvantages or at least to reduce said disadvantages.
In agreement with said object the invention now provides a control or measuring unit of the type mentioned in the heading paragraph which according to the invention is characterized in that
the receiving coils are made onto or into a first substrate,
the transmitting coil is made or into a second substrate,
one of the substrates is connected to the control or measuring means and is together therewith in relation to the other substrate which is located at a fixed position,
the spring forces are acting onto the control or measuring means respectively onto the substrate connected to said control or measurings means such that the control or measuring means has at least two freedom degrees,
the transmitting coil and receiving coils being embodied such that therewith unique combinations of output signals, characteristic for each of the freedom degrees of the control or measuring means, can be generated.
It is remarked that a switching unit, comprising two mutually movable substrates carrying combinations of transmitting and receiving coils is described in the U.S. Pat. No. 4,425,511. Although this prior art unit does not comprise ferromagnetic bodies or berate bodies, resulting into the therewith corresponding advantages, the control means of this prior art unit is only movable in one direction, i.e. the unit has only one degree of freedom, and furthermore the various coils and the therewith connected detection circuit are embodied such that only the movement according to this one degree of freedom can be detected.
For generating the electromagnetic field the transmitting coil has to be connected to an oscillator circuit receiving energy from a suited power supply source. Although it is certainly conceivable to install an oscillator circuit together with a small battery onto the first substrate (and eventually on the third substrate) it will be clear that the presence of the battery will induce heavy rejections. It is therefore preferable that the energy for generating the electromagnetic field is supplied by an oscillator circuit installed onto the first substrate and connected to the transmitting coil or transmitting coils through conductors onto said substrate, and connected with a power supply source at a fixed position through flexible conductors between the substrate and the fixedly positioned power supply source.
In case the application of a flexible connection between the movable substrate and the power supply source, installed at a fixed position, meets objections then these objections can be eliminated in that the energy for generating the electromagnetic field is supplied by an oscillator circuit installed onto the second or third substrate and coupled through a transformer circuit comprising a primary winding on the second or third substrate and a secondary winding on the first substrate, to the transmitting coil(s) onto the first substrate.
A rather simple embodiment of the first substrate (and eventually of the third substrate) is characterized in that the secondary coil, the transmitting coils and the conductors running therebetween are realized by means of an electrically conducting first respectively third substrate of non-ferro magnetic material, in which at the coil locations openings are made, the shape and dimensions of which are corresponding to the shape and dimensions of the respective coil, whereby the openings, realizing said transmitting coils, are through slots connected to an opening by means of which the secondary transformer coil is realized.
The fabrication process of the first (and eventually third) substrate is thereby reduced to a simple blank or punch operation.
To obtain an at least approximate linear variation in the signal, especially during rotation of the first substrate around the central axis of the control handle (rotation in the X-Y-plane) preferably each transmitting coils is divided into a number of coil sections, the number of which corresponding to the number of receiving coils and each section cooperating with one receiving coil, or by each coil section comprises a stretch which in the neutral position of the unit runs parallel to part of the cooperating receiving coil, and furthermore conducting paths through which said stretches are mutually coupled.
The disadvantages of the restricted number of freedom degrees can be eliminated in various ways. A proposed embodiment, comprising a first substrate with transmitting coil(s) and a second substrate with receiving coils, installed at a fixed position, is characterized in that the spring forces biasing the control or measuring handle towards the neutral position, are generated by tension springs attached between attachment points on the first substrate and attachment points on the frame or housing of the control are measuring unit. The use of a number of tension coils, preferably acting into one plane, at least in the neutral position of the unit, has the advantage that rotations around each of the X, Y and Z-axes are possible, that the control handle is movable in a direction parallel to itself in each of the axis direction and also combined translational and rotational movements are possible.
A further embodiment, proposed in relation to an extension of the number of freedom degrees, is characterized by the spring forces for biasing the control or measuring handle towards a neutral position are generated by a cylindrical helical spring, one end of which is attached to the underside of the control or measuring handle and the other end of which is attached at a fixed position to the frame or housing of the control or measuring unit such that the central axis of this cylindrical helical coil coincides with the central axis of the control or measuring handle in the neutral position thereof.
Also in this embodiment a rotation around the X and Y-axis is possible as well as a translational movement in the Z-direction, whereas dependent onto the spring characteristic also a rotation around the Z-axis and in a restricted manner also a translational movement in the X and Y-direction are possible. Although the movement possibilities are in this case rather restricted, the construction is very simple.